1. Field of the Invention
The present invention relates, in general, to heat pump type air conditioning apparatuses and, more particularly, to an improvement in such apparatuses to accomplish a desired evaporation efficiency of gaseous refrigerant returning to a compressor during a heater-mode operation of such an apparatus.
2. Description of the Prior Art
As well known to those skilled in the art, a heater-mode operation of a known heat pump type air conditioning apparatus is performed with the refrigeration cycle of a cooler-mode operation of the apparatus being reversed. However, the evaporation efficiency of gaseous refrigerant during such a heater-mode operation may be reduced when atmospheric air has a low temperature. Such a low temperature atmospheric air thus results in a lacking of heating calories during a heater-mode operation of such an air conditioning apparatus. This reduces the room heating effect of the apparatus when the temperature of atmospheric air is low in days of cold weather. Heat pump type air conditioning apparatuses capable of overcoming this problem have been actively studied recently.
Known heat pump type air conditioning apparatuses, designed to overcome the above-mentioned problem, are referred to in Japanese Utility Model Publication No. Sho. 49-18927 and Japanese Patent Publication No. Sho. 54-45949. In the air conditioning apparatus of No. 49-18927, main and auxiliary indoor heat exchangers are installed in a refrigeration circuit. In a cooler-mode operation of the apparatus, one of the two indoor heat exchangers is used as an evaporator for vaporizing refrigerant, with the other heat exchanger being stopped. Meanwhile, during a cooler-mode operation, all the two indoor heat exchangers are used as condensers for heating room air. On the other hand, in the air conditioning apparatus of No. 54-45949, a refrigerant heater is mounted on a refrigeration circuit. The above refrigerant heater is used as an evaporator during a heater-mode operation of the apparatus. During such a heater-mode operation of the apparatus, the highly-pressurized, hot gaseous refrigerant from a compressor is condensed and liquidized at an indoor heat exchanger while heating room air. Thereafter, the refrigerant is reduced in pressure at a heater-mode capillary tube, thus becoming a low pressure refrigerant. The low pressure refrigerant from the heater-mode capillary tube is, thereafter, vaporized at the refrigerant heater, thereby accomplishing a desired room heating effect even when the atmospheric air has a low temperature.
However, the apparatus of No. 49-18927 is problematic in that the two indoor heat exchangers, selectively used as a condenser during a heater-mode operation, are designed to use the compressor as a heat source when the two indoor heat exchangers heat the room air. This forces the apparatus to use a large capacity compressor and results in an increase in the production and maintenance cost of the apparatus. Another problem of the apparatus resides in that the volume of the indoor heat exchangers is exceedingly enlarged. Therefore, the apparatus needs a large area for installing the indoor heat exchangers and this gives a limitation on where the apparatuses may be installed due to insufficient area.
On the other hand, the apparatus of No. 54-45949 has the following problems. That is, the document discloses that a refrigerant heater is selectively used as an evaporator during a heater-mode operation of the apparatus. However, the document fails to describe the construction of the refrigerant heater in detail. When designing the apparatus while considering the structural limit of a conventional evaporator, it is necessary for those skilled in the art to use a typical electric heater as the refrigerant heater since the electric heater has a small volume and is easily installed. However, such an electric heater regrettably increases the maintenance cost of the air conditioning apparatus.